Field of the Disclosure
The present application relates to a control device for a supercharged engine, and particularly relates to the control device for the supercharged engine capable of reduced cylinder operation (cylinder cutoff operation) that stops operation of one or more cylinders of the engine.
Description of the Related Art
Japanese Patent Laid-Open No. 2006-307677 and Japanese Patent Laid-Open No. 2009-250068 as follows disclose arts relating to control of supercharged engines capable of reduced cylinder operation. Further, each of the supercharged engines disclosed in these patent applications includes a plurality of intake passages in which compressors are placed, and a common intake passage (a surge tank) formed by combining the intake passages.
The supercharged engine described in Japanese Patent Laid-Open No. 2006-307677 is a V12 engine including six cylinders in each of a left and a right bank. The six cylinders in each of the banks are grouped into two cylinder groups, each cylinder group is formed of three cylinders, and four cylinder groups in total are created. Four turbochargers in total are provided, one for each of the cylinder groups. The compressors of the respective turbochargers are placed in four intake passages which are independently provided. The four intake passages join in one surge tank, and the surge tank is commonly used among all cylinders. A turbine of each of the turbochargers is placed in an exhaust manifold that is provided for each of the cylinder groups.
In the supercharged engine described in Japanese Patent Laid-Open No. 2006-307677 and having a configuration as described above, the reduced cylinder operation is performed in each of the cylinder groups as a unit. However, since the four cylinder groups commonly use one surge tank, there is a fear that backflow of air through the compressor corresponding to the cylinder group will occur, to which the reduced cylinder operation is applied, depending on a pressure condition when the engine is switched to reduced cylinder operation. In this regard, in the supercharged engine, one of the conditions required for executing the reduced cylinder operation is a pressure condition under which, pressure of a downstream side of the compressor is equal to or lower than predetermined minimum pressure, that is, the backflow does not occur even if the operation is switched to the reduced cylinder operation.
According to the reduced cylinder operation, equal torque can be realized by fewer cylinders. Therefore, thermal efficiency of the engine as a whole is enhanced, and fuel efficiency can be enhanced. Consequently, enlarging an operating region in which the reduced cylinder operation is performed is desired from a viewpoint of fuel efficiency performance.
However, since the supercharged engine described in Japanese Patent Laid-Open No. 2006-307677 has the pressure condition as described above, the reduced cylinder operation cannot be performed in a high load region in which supercharging pressure is high. That is to say, the operating region in which the reduced cylinder operation can be performed is restricted, and the effect of increasing fuel efficiency by reduced cylinder operation cannot be sufficiently obtained. A similar problem can also arise in the supercharged engine described in Japanese Patent Laid-Open No. 2009-250068.